Field of the Invention. The present invention relates to a portable microscope for use in inspecting fiber optic connections, and more particularly, to a portable microscope with a battery powered light source. The portable microscope is provided with a metal end plate with a highly reflective bowl to increase the intensity of the light for improving the view of the fiber optic cable secured in a connector. The end plate may also be provided with adapters to accommodate different sizes of ferrules used in the fiber optic connectors. Rocker heads may be attached to the end plate to facilitate the viewing the end of fiber optic cables at different viewing angles.
Summary of Related Art. Fiber optic technology is the transmission of energy by light through glass fibers, and is used to transmit and receive analog and digital signals. Fiber optic technology is now being woven into the network of telephones, televisions, computers, and data banks that form the information super highway. Fiber optic cable is the premier medium to meet the demand for higher speeds and greater information carrying capacity. Telephone, cable television, communication companies, and other businesses around the world are investing billions of dollars in fiber optic lines which have an enormous capacity for carrying data.
Fiber optic systems can be used to replace and enhance electronic or electrical systems in a number of applications, including process control systems, security systems, cable television, high speed switching circuits, motor control circuits, video links and various LAN networks. Because of the advantages of fiber optic systems over conventional electrical and electronic components and systems, significant growth and expansion is anticipated in the use of fiber optic systems.
One of the main advantages of the fiber optic system is the ultra clear and clean signals in such system. Fiber optic systems are non-conductive, and are not effected by interference from radio frequency or electromagnetic fields. A fiber optic system can be routed through high voltage areas and radio-microwave communications systems without any noise shielding. A fiber optic system poses no electrical hazard potential, and can be used in explosive or fire hazard areas. A fiber optic system has a much greater range of temperature stability and is less susceptible to the adverse affects of moisture.
The losses associated with the transmission of fiber optic signals are significantly less than the losses in an electrical system. The fiber optic signals travel greater distances without amplification. An amplified fiber optic signal is preferred over conventional cable signals because the fiber optic system has little or no induced noise in the amplified signal.
Another major benefit of a fiber optic system is the greater information carrying capacity. The fiber optic cable is significantly smaller and lighter in weight than the comparable copper conductors required for equivalent transmission capabilities. Coaxial cable used for cable television application can carry approximately 10 million bits of data per second. Comparable fiber optic cables, in contrast, can carry data at more than 10 gigabits (10 trillion bits) per second. Optical data is transmitted through fiber optic cable at speeds up to 100 times faster than data transmitted using copper wire.
A typical fiber optic system consists of a transmitter, a transmission medium, and a receiver. The transmitter receives an analog or digital electrical input signal and includes a source driver and light source to generate and transmit a light signal. The source driver receives the electrical input signals and generates control signals to control the light source. The typical light sources are lasers or light emitting diodes. The light from the light source is transmitted through the transmission medium to the receiver. The receiver is an optical detector which converts the light signal back into the same form of electrical signal as the original input.
The transmission medium is a fiber optic cable which includes a core made from extremely pure glass drawn out into a fine strand that is strong and flexible. The fiber optic cable also requires an outer sheath or cladding formed around the highly transparent core of glass that carries the light. The cladding reflects light back into the core such that the light is propagated by internal refraction. Fiber optic cable is classified by transmission type (single mode, graded index multimode, etc.) and by core/cladding diameter (i.e. 62.5/125 microns).
The single mode fiber only propagates one mode of light which makes it highly efficient. This type of cable is used with laser sources and requires an exact coupling alignment to a well-defined beam of light. The graded index multimode fiber exhibits a variable core density cross-section, which reduces intermodal dispersion and acts to focus broader bandwidths of reflected light into the fiber's core. Precision alignment of splices and connections are also essential in the graded index multimode fiber.
A single mode cable consists of a single glass fiber core surrounded by a layer of cladding, a buffer, a strength member, and an outer protective covering. The cladding is formed by doping one or more layers of glass. The cladding has a lower index of refraction than the glass which causes a light wave to be directed by towards the core of the fiber optic cable. In a multiple mode configuration, the core is made up of multiple layers of glass. Each layer is doped to exhibit a slightly lower index of refraction than the previous layer.
The buffer adds strength and stability to the fiber and may be made from a variety of materials, such as polyvinyl. The strength member protects the fiber during installation and use, and is made from a strong, flexible material. The outer cover is typically made from plastic and protects the core of the cable from ambient conditions.
The single mode and/or multiple mode fibers can be assembled into multi-fiber bundles with a single outer cover. The bundles may include a central strength member for additional strength during installation. The bundle is designed to facilitate the splitting out of individual fibers for connection purposes.
The core size may be as small as 10 microns in diameter for a single mode fiber and as large as 85 microns for a multiple mode fiber. When the cladding is included, the total diameter for a single mode fiber can range up to 125 microns. The single mode fiber is very efficient at transmitting light, but such fiber has a small numerical aperture and is not effective in gathering light. Consequently, the single mode fiber is generally used for long distance applications with laser light transmitters, which can provide a concentrated beam of light. The multiple mode fiber has a much larger numerical aperture, but is less efficient at transmitting the light. The multiple mode fibers are used with light emitting diodes for with a broader light wave for more local applications (50 miles or less). The diameter for multi mode fibers ranges from 125 microns to 400 microns.
Attenuation is the loss of power that a light pulse experiences from the source to the receiver. The attenuation in a fiber optic system is measured in decibels. Attenuation may be caused by dispersion, fiber defects, improper installation and maintenance, and other similar factors.
In fiber optic systems, designer engineers and technicians perform power budget calculations to determine original and periodic operational system integrity in regard to attenuation. The transmitter spectral output power and receiver maximum sensing range are compared to the system losses in the fiber, connectors, spices, and couplers. The transmitter and receiver must be sized to ensure power to propagate the signal from the source to the receiver.
The total attenuation is significantly affected by the quality of the connections and/or splices in the fiber optic system. The losses at a dirty or poor quality connection can easily increase losses in the fiber optic system by as much as ten times the projected amount for a high quality connection. Poor quality connections are the most frequent cause of power loss, which results in operating defects and breakdowns in the fiber optic system.
Each fiber optic system will have optical connections at each junction between a fiber optic cable and a light source or detector. Connections are also needed to join or splice together the ends of two cables. Since each fiber optic system will include a number of junctions of fiber optic cable, it is essential that the technicians working on fiber optic cables in the field use a microscope and other tools to properly connect the fiber optic cables.
In the installation of a fiber optic system, transmitters and receivers may be positioned throughout the system at the desired locations for transmitting and receiving signals. The transmitters and receivers are mounted in a light interface unit which includes both electrical receptacles for input/output of electrical signals and lighting receptacles for the input/output of light signals. After the light interface units with transmitters and receivers have been installed and the cable between the light interface units pulled, one of the final field steps to complete the installation is connectorization, which is the connection of fiber optic connectors to the ends of the fiber optic cables to facilitate the proper alignment of the core of the fiber optic cable at the fiber optic connections.
In a fiber optic system, a receptacle is a termination device for a fiber optic connection. The receptacle has two ports aligned with a center aperture to promote proper alignment of the fiber optic cable cores at the point of connection. In a light interface unit, the receptacle is mounted in a fixed position with one port connected to a transmitter or receiver and the second port aligned for the insertion of a connector on the end of the fiber optic cable. Receptacles are also used outside of the light interface units to splice together two fiber optic cables.
The fiber optic cables used in a system will have a connector secured to each end of the fiber optic cable, the connector being designed for insertion and locking in the receptacle. The cable is stored on spools and is pulled from the spools in the field during installation. Several different types of receptacles and connectors are available for use in fiber optic systems.
The connectors are typically installed on the fiber optic cable in the field at the time of installation. The fiber optic cable is stripped of its protective covering and the glass core and cladding are inserted into the connector such that the glass core extends from the ferrule at the end of the connector. The cable is epoxied into the connector and the glass core at the end of the ferrule is cleaved and polished using a lapping process.
The polished end of the core of the cable must be inspected to ensure that the end surface is clean and scratch free. Any scratches or cracks in the end of the glass fiber will adversely effect the integrity of the connection. Even body oils, lint or dust can cause unacceptable losses at the connection.
Because the glass core of a fiber optic cable is so small and because a good connection is essential to the overall efficiency of the system, a portable microscope for use in connecting the connectors to the fiber optic cable is an essential tool for the technician. The technician in the field must be able to inspect the end of the core of the fiber optic cable to ensure a smooth and clean surface for transmission of the light.
As the application of fiber optic systems for business and personal use has increased, the demand for technicians to install and service the systems has not kept pace. In addition, there is a critical need for tools and supplies which are suited for use by technicians in the installation and servicing of the fiber optic systems.
One of the problems with existing portable microscopes is providing sufficient lighting directed to the core of the fiber optic cable when positioned at the end of the microscope. The light source on a portable microscope is not very powerful and cannot be positioned in the most desirable position.
Another problems with existing portable microscopes is the dark plastic heads used to position the end of the fiber optic cable. The heads have a tendency to break or crack during use in the field. The dark surface of the plastic head tends to absorb light and adversely impact the ability of the technician to inspect the end of the fiber optic cable.